mc68331cpv20b1 Freescale Semiconductor, Inc, mc68331cpv20b1 Datasheet - Page 93

• Manufacturer Part Number: mc68331cpv20b1
• Description: Mc68331 32 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

4.8.1.1 Chip-Select Pin Assignment Registers
MC68331
USER’S MANUAL
The pin assignment registers contain twelve 2-bit fields (CS[10:0] and CSBOOT) that
determine the functions of the chip-select pins. Each pin has two or three possible
functions, as shown in Table 4-19.
Table 4-20 shows pin assignment field encoding. Pins that have no discrete output
function do not use the %00 encoding.
Port size determines the way in which bus transfers to an external address are allo-
cated. Port size of eight bits or sixteen bits can be selected when a pin is assigned as
a chip select. Port size and transfer size affect how the chip-select signal is asserted.
Refer to 4.8.1.3 Chip-Select Option Registers for more information.
Out of reset, chip-select pin function is determined by the logic level on a correspond-
ing data bus pin. These pins have weak internal pull-up drivers, but can be held low
by external devices. (Refer to 4.6.3.1 Data Bus Mode Selection for more informa-
tion.) Either 16-bit chip-select function (%11) or alternate function (%01) can be select-
ed during reset. All pins except the boot ROM select pin (CSBOOT) are disabled out
of reset. There are twelve chip-select functions and only eight associated data bus
pins. There is not a one-to-one correspondence. Refer to 4.8.4 Chip-Select Reset
Operation for more detailed information.
The CSBOOT signal is normally enabled out of reset. The state of the DATA0 line dur-
ing reset determines what port width CSBOOT uses. If DATA0 is held high (either by
the weak internal pull-up driver or by an external pull-up device), 16-bit width is select-
ed. If DATA0 is held low, 8-bit port size is selected.
Chip Select
CSBOOT
16-Bit
Table 4-20 Pin Assignment Field Encoding
CS10
CS0
CS1
CS2
CS3
CS4
CS5
CS6
CS7
CS8
CS9
Freescale Semiconductor, Inc.
Bit Field
Table 4-19 Chip-Select Pin Functions
For More Information On This Product,
00
01
10
11
SYSTEM INTEGRATION MODULE
Chip Select
Go to: www.freescale.com
CSBOOT
CS10
8-Bit
CS0
CS1
CS2
CS3
CS4
CS5
CS6
CS7
CS8
CS9
Chip Select (16-Bit Port)
Chip Select (8-Bit Port)
Alternate Function
Discrete Output
Description
Alternate
Function
CSBOOT
ADDR19
ADDR20
ADDR21
ADDR22
ADDR23
BGACK
FC0
FC1
FC2
BR
BG
Discrete
Output
ECLK
PC0
PC1
PC2
PC3
PC4
PC5
PC6
—
—
—
—
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